The present invention relates in general to a motor drive control system responsive to external command signals for controlling an operation of a motor, and more particularly to such motor drive control system capable of restricting a temperature rise of the motor below a predetermined upper limit.
In the art of controlling a motor such as a DC motor in repeatedly or intermittently actuated manner in response to external command signals, it has been required to hold a temperature rise of the motor below a preset permissible level. To meet this requirement, it has been attempted to use a motor with a larger capacity or to provide a DC motor with a cooling device. However, such attempts necessarily suffer from problems; unnecessarily bulky or large-sized structure for increased capacity of the motor; complicated construction and increased operating noises due to the provision of a cooler; etc. In the meantime, there have been proposed some remedies or solutions to these problems. For example, a temperature sensor is provided for monitoring an operating temperature of the CD motor to turn off the motor upon temperature rise beyond a preset upper limit. In this arrangement, the DC motor is stopped unexpectedly regardless of the external command signal produced to operate the motor. Further, the motor which has been thus stopped must be kept at rest for a comparatively long period of time so that the motor temperature can be lowered enough to re-activate the motor. Thus, this solution is not completely satisfactory. It is also known to provide means for limiting an operating interval, i.e., the number of intermittent operations of a DC motor per unit time according to known operating characteristics of the specific motor, that is, to provide means for preventing the motor from repeating a start and stop cycle at a frequency higher than a preset limit. This arrangement is also inconvenient because it suffers unnecessary limitation in the number of intermittent operations of the motor that can be conducted within a given periof of time. According to a Japanese patent application No. 56-165916 filed Oct. 16, 1981 in the name of the assignee of the present invention, a method is proposed which is free from the above discussed inconveniences, in which a motor is neither unnecessarily limited in the number of operations per unit time, nor subject to an unexpected stop or a requirement for extra capacity or the provision of a cooling device. Although the above method is thus effective, it requires the detection of the angular position and rotating speed of the motor during rotation thereof and at the same time the measurement of a rotating time thereof, thereby inherently complicating a control circuit. Thus, the known methods are still disadvantageous.